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Authors: B. De Geyter, P. Geiregat, A. J. Houtepen, D. Van Thourhout, L. Siebbeles, Z. Hens
Title: Ultrafast Photoinduced Intraband Absorption in PbS, PbSe and PbSe/CdSe Core/Shell Nanocrystals for near-Infrared to Mid-Infrared All-Optical Signal Processing
Format: International Conference Presentation
Publication date: 11/2011
Journal/Conference/Book: MRS Fall Meeting 2011
Editor/Publisher: Materials Research Society, 
Location: Boston, United States
Citations: Look up on Google Scholar
Download: Download this Publication (233KB) (233KB)


Colloidal nanocrystal quantum dots and dot-in-dots are highly tunable optical materials due to strong quantum confinement of the carriers. The quantum confinement not only raises the bandgap energy, it also relaxes intraband selection rules, making multicarrier Auger recombination ultrafast and optical dipole transitions between intraband states allowed. We present a transient absorption study which shows that photoinduced absorption below the bandgap in PbS, PbSe and PbSe/CdSe colloidal quantum dots can be attributed to intraband absorption. The power dependence agrees with a state-filling model of the bandgap excitonic states and the dynamics of the absorption decay indicate that initial state population decays through Auger recombination. The strength of the intraband transition is wavelength-independent up to (at least) 2000 nm and is about 10% of the bandgap transition strength. The broadband nature, the ultrafast dynamics and the high cross section make these material excellent candidates for all-optical high-speed signal processing on the silicon photonics platform in both the near and the mid-infrared wavelength range.

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